效果：

292112114761462b79ca271477fac98.jpg

<view class="fixbot_btn" @click="downloadImgs">批量保存到相册</view>
<script>
import { writePhotosAlbum } from '../../utiils/util.js'

// 下载图片
            downloadImgs() {
                this.clicked = false
                if (this.checkUrl.length === 0) {
                    this.clicked = true
                    wx.showToast({
                       title: '请选择需要保存的图片',
                       icon: 'none'
                    })
                    return
                }
                if (this.checkUrl.length > 9) {
                    this.clicked = true
                    wx.showToast({
                       title: '每次最多只能保存9张图片',
                       icon: 'none'
                    })
                    return
                }
                var _this = this
                // 获取保存到相册权限
                writePhotosAlbum(
                    function success() {
                        // 调用保存图片promise队列
                        _this.queue(_this.checkUrl).then(res => {
                            wx.hideLoading()
                            wx.showToast({
                               title: '下载完成'
                             })
                            _this.imgList.forEach((item, i) => {
                                item.checked = false
                            })
                            _this.checkUrl = []
                            _this.clicked = true
                    }).catch(err => {
                        _this.checkUrl = []
                        _this.clicked = true
                        wx.hideLoading()
                    })
                },
                function fail() {
                    wx.showToast({
                     title: '您拒绝了保存到相册',
                     icon: 'none'
                    })
                    _this.clicked = true
                })
            },
            // 队列
            queue(urls) {
                let promise = Promise.resolve()
                urls.forEach((url, index) => {
                    promise = promise.then(() => {
                        return this.download(url,index)
                    })
                })
                return promise
            },
            // 下载
            download(url, index) {
                let length = this.checkUrl.length
                return new Promise((resolve, reject) => {
                    wx.downloadFile({
                        url: url,
                        success: function(res) {
                            var temp = res.tempFilePath
                            wx.saveImageToPhotosAlbum({
                                filePath: temp,
                                success: function(res) {
                                    wx.showLoading({
                                        title: '下载中(' + (index + 1) + '/' + length + ')'
                                    })
                                    resolve(res)
                                },
                                fail: function(err) {
                                    reject(res)
                                }
                            })
                        },
                        fail: function(err) {
                            reject(err)
                        }
                    })
                })
            },
<script>

util.js

//保存图片到相册
export const writePhotosAlbum = (successFun,failFun) =>{
  wx.getSetting({
    success(res) {
      if (!res.authSetting['scope.writePhotosAlbum']) {
        wx.authorize({
          scope: 'scope.writePhotosAlbum',
          success: function () {
            successFun && successFun()
          },
          fail: function (res) {
            wx.hideLoading()
            wx.showModal({
              title: '提示',
              content: "小程序需要您的微信授权保存图片，是否重新授权？",
              showCancel: true,
              cancelText: "否",
              confirmText: "是",
              success: function (res2) {
                if (res2.confirm) { //用户点击确定'
                  wx.openSetting({
                    success: (res3) => {
                      if (res3.authSetting['scope.writePhotosAlbum']) {
                        //已授权
                        successFun && successFun()
                      } else {
                        failFun && failFun()
                      }
                    }
                  })
                } else {
                  failFun && failFun()
                }
              }
            });
          }
        })
      } else {
        successFun && successFun()
      }
    }
  })
}